Explosive suspension

ABSTRACT

An explosive suspension used in blasting operations such as, but not limited to, mining operations and the like, composed of ammonium nitrate (AN) based explosives incorporating a solid fuel material and a suspending agent. The suspension comprises an oxidizer component, a solid fuel material, optionally up to 10 weight % of a liquid fuel component, and a suspending agent. The solid fuel material comprises vitrinite macerals, liptinite macerals, and inert macerals fusinite and semifusinite, and is characterized as (1) having a concentration of liptinite that is higher than normal coals, and (2) having a concentration of pseudovitrinite that is significantly lower than normal coals.

FIELD OF THE INVENTION

The present invention relates generally to the field of explosive compositions and methods of formulating same. More particularly, the present invention provides a multi-component explosive suspension which is useful in blasting operations such as, but not limited to, mining operations and the like. More especially, the present invention relates to the manufacture and use of suspensions of nitrate explosives, commonly referred to in the industry as “emulsions,” for example ammonium nitrate (AN) based explosives.

BACKGROUND OF THE INVENTION

Blasting operations in quarry mining and open pit mining conventionally use ANFO-based explosives. ANFO is a stoichiometric mixture of ammonium nitrate and fuel oil, which corresponds to approximately 94 wt % AN and approximately 6 wt % fuel oil. While ANFO remains a popular explosive in the industry, it has limitations, for example limited control over velocities of detonation (VOD), generation of toxic NOx gases if under-fueled, poor storage stability arising from inadequate mechanical stability and instability to water exposure, lower density than water, thus not allowing for displacement of water in wet boreholes, limited packaging options, as well as unprecedented increases in the price of ammonium nitrate.

A need exists in the art, therefore, for other explosive formulations which are as effective as ANFO or more effective than ANFO in their explosive effect. The present invention seeks to meet needs, including enhanced control over velocities of detonation (VOD), shifting the oxygen balance away from NOx-producing conditions, increased storage stability arising from improved mechanical and chemical stability, higher density than water allowing for displacement of water in wet boreholes, and the ability to package in tubes and other formats.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, the present invention provides a nitrate based explosive formulation, for example an AN-based explosive formulation, in the form of a suspension, which principally comprises AN, a liquid fuel component, a solid fuel material, and a suspending agent. The suspensions of the invention are capable of reducing VOD, and are mechanically stable, water resistant, and produce results which are as good as or better than those obtained using conventional explosives.

More specifically, the present invention provides an explosive suspension comprising a nitrate, for example, 30-95% ammonium nitrate, 0-10 wt %, more usually less than 8 wt %, for example 2-8 wt % by weight of liquid fuel, 5-80 wt % solid fuel material, and 0-10 wt % of at least one suspension agent. The formulation may optionally also contain materials including water, inorganic oxidizers, bulking agents, among other materials. In one embodiment, the carbon and hydrogen atoms in the liquid fuel that are chemically necessary for an optimum blast are replaced in the current suspensions with the solid fuel material characterized as (1) having a concentration of liptinite that is higher than normal coals, and (2) having a concentration of pseudovitrinite that is significantly lower than normal coals.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to multi-component explosive suspensions which are useful in blasting operations such as, but not limited to,mining operations and the like. However, it will be understood that these explosive suspensions can be applied to other blasting operations.

More specifically, the present invention relates to suspensions of AN-based explosives comprising a solid fuel material and a suspending agent. In one particular aspect, the present invention provides an explosive formulation comprising or consisting of an oxidizer, a solid fuel material, a liquid fuel, and a suspending agent. The formulation may optionally also include materials including water, inorganic oxidizers, bulking agents, among other materials.

Each component of the present suspension is individually not an explosive. As such, each component can be handled, shipped and stored as oxidizers, flammable materials, or other suitable classes less hazardous than explosives. Such classifications are shipped more easily, safely, and less expensively than explosives. However, it will be understood that these components, when mixed, form an explosive mixture which may be used in blasting operations such as, but not limited to, mining operations and the like.

The first component of the suspension of the present invention is an oxidizing compound. The oxidizing compound can be selected from oxidizers conventionally used in the manufacture of explosive compositions to achieve desired properties. Examples of oxidizers are anionic oxides of nitrogen, sulfur, and carbon (such as nitrate, sulfate, and carbonate), permanganate anion, chromate anion, diatomic oxygen (O₂), ozone, and peroxides. The preferred oxidizer is a nitrate compound, for example ammonium nitrate. For purposes of formulating suspensions, the AN need not be “prilled,” but rather can be blended into the formulation as a dry, granular powder or as a solution. In comparison, the nitrate compound in ANFO is typically manufactured and delivered as a coated spheroid or prill that is has a typical diameter of about 0.02 to 0.1 inch.

The second component of the suspension is liquid fuel component, for example a liquid fuel component conventionally used in the manufacture of explosive compositions to achieve desired properties. The second component may or may not be present. Thus, the second component may be present in an amount of about 0-10% by weight, for example 2-8% by weight. As used herein, all weights and percent by weight are based on total weight of the formulation. In one embodiment, the second component is a flammable or combustible liquid. Such liquids include, but are not limited to, hydrocarbon-based liquid fuels, including petroleum-derived products (e.g., fuel oils, diesel, kerosene, gasoline, alkanes, alkenes, and blends thereof), oxygen-containing liquid fuels such as alcohols, glycols, ethers, ketones, etc. (e.g., methanol, ethanol, n-propanol, iso-propanol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, glycerin, polyglycols, polyethers, and blends thereof)

Conventional ANFO generally comprises a mixture of ammonium nitrate and about 6% by weight of fuel oil. The current formulation may comprise the first dry component and, if present, less than 10% by weight, for example 2-8 wt %, of the liquid second component. The quantity of the liquid second component may be further reduced with an increase in the concentration of the solid fuel component as further described below.

The carbon and hydrogen atoms contained in the liquid fuel that are chemically necessary for an optimum blast are at least partially replaced in the current suspensions with the third component of the composition, namely a solid fuel material. Typically, the solid fuel material has a high carbon and hydrogen content, a high melting point, and is pyrolyzable and combustible. Solid fuel materials include those materials composed primarily of carbon and hydrogen, and optionally contain oxygen and other heteroatoms that can be combusted in the presence of an oxidizer. Examples of solid fuel materials include, but are not limited to, certain coals, polymers/plastics such as polyethylene and polypropylene, paraffin waxes, and possibly rubber from tires.

In the disclosed formulation, the third component is coal with specific properties, defined further herein. The main maceral component (approximately 75%) of the third component is vitrinite. Also included are the liptinite macerals sporinite, cutinite and resinite. The inert macerals fusinite and semifusinite are also present in the third component. As used herein, the term “maceral” means those organic units that comprise coal. As such, coal is composed of macerals which each have a distinct set of physical and chemical properties that dictate the behavior of the coal.

The third component may be further characterized in that the amount of liptinite macerals, particularly cutinite, is higher than normal, and almost no pseudovitrinite (structured coalified wood) is present in the third component. The vitrinite group generally includes two sub-groups namely matrix vitrinite, also known as desmovitrinite, and pseudovitrinite, also known as telovitrinite. The normal amount of vitrinite macerals in coal is similar to the amount of vitrinite macerals in the third component, approximately 75% by weight. However, of the total 75% by weight of vitrinite macerals found in coal, the normal amount of sub-group pseudovitrinite present is between 25-35%. In contrast, of the total 75% by weight of vitrinite macerals in the third component, there is little trace, near zero, amount of pseudovitrinite present.

Acceptable specimens of the third component may be found in the Friendsville Coal Seam at the base of the Mattoon Geological Formation and within the McLeansboro Group of the Missourian Series of the Pennsylvanian Geologic System of sedimentary rock of Southeastern Illinois. However, alternate solid fuel materials having the characteristics as described above can also be used.

The inherent chemical and physical properties of the third component, as described and used with the first and second components, allows for suitable blasting properties, for example, velocities that match or exceed the natural resonant frequencies of those materials being blasted thereby utilizing only the energy required to fragment and move the rock, and do so in a safe and efficient manner.

The particle size of the solid fuel material to be incorporated into the suspension may range from a fine powder to ½ inch diameter chip, preferably below ⅜ inch. Blast characteristics can be altered by particle size within the suspension, in that smaller particles are more rapidly combusted than larger particles due to high surface area. Viscosity and other properties of the formulation can also be altered by selection of particle size. For example, when a very fine particle size is added to the formulation, it acts as a viscosity modifier, increasing the viscosity of the product dramatically.

The fourth component is a suspending agent for facilitating uniform blending of the composition as a suspension. Suitable suspending agents include polymeric and nonpolymeric emulsifiers or mixtures thereof, and are present in concentrations up to 10%, typically less than 5%. The suspending agents may be selected and blended to achieve desirable properties, such as increasing the stability of the emulsion before and after homogenization. Examples of polymeric and nonpolymeric emulsifiers include, respectively, those based on various adducts of polyisobutenyl succinic anhydride (PIESA), and those such as sorbitan monooleate (SMO).

The above-discussed components of the present suspension may be packaged in separate containers conventionally employed for the desired purpose. Mixing of the components to form the suspensions can be accomplished using mixing means known in the art.

As discussed, the present suspensions comprise an admixture of a first component (the oxidizer), optionally a liquid second component, a third solid fuel material, and a fourth suspending agent. The liquid second component is generally present in an amount of about 0-10% by weight, for example 2-8% by weight.

The concentration of the second component in the present formulation may represent a decrease in volume of the liquid component used when compared with conventional explosives. The carbon and hydrogen atoms in the second component chemically necessary for an optimum blast are replaced in the current formulation with the third component. Application of a lesser volume of the liquid second component as described reduces the cost of the present explosive suspension compared with presently available explosive compositions. Similarly, inclusion of the third component as discussed depletes the required volume of the first component which further reduces the cost of the present explosive formulation compared with presently available explosive compositions.

The blend ratio of the third component can be altered to more closely match the VOD of the explosive with the estimated natural resonant frequency of the material to be blasted. The third component can be blended in ranges of about 5% to 80% of the total weight of the suspension. The suspension is loaded and delayed, and the shot is initiated according to conventional methods.

EXAMPLES

In a specific example, approximately 25 wt % of the solid fuel material was blended with a commercially available, unsensitized emulsion and loaded in two holes of a production shot at a coal mine. Borehole depth was approximately 100 feet. Velocities of detonation for the disclosed suspension were monitored and are included in the table below. By comparison, typical VODs for commercially-available, sensitized emulsions range from 16,000 to 18,000 feet per second (fps), which is often much faster than required, and may result in unfavorable results:

Weighted Initial Intermediate Final VOD Ave VOD Hole # VOD (fps) VOD (fps) (fps) (fps) 1^(a) 11,100 6,500 11,000 8,700 2^(b) 9,500 6,200 13,000 9,500 ^(a)Through first 40 ft of borehole. ^(b)Through entire 100 ft borehole.

Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention. For example, the present formulation was described with particular reference to the use of AN-based explosives in surface mining. However, it is to be noted that the present invention is not limited to the production and use of this type of explosive, but rather the scope of the present invention is more extensive so as to also include materials, modifications and applications other than those specifically described. Further, it will be clear that embodiments described may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the present invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. An explosive suspension comprising: a dry, granular, solid component, or solution thereof, a solid fuel material, and a suspending agent, wherein said solid fuel material contains a vitrinite maceral, liptinite maceral, and inert macerals fusinite and semifusinite, and wherein the amount of liptinite macerals is higher than normal, and wherein almost no pseudivitrinite is present in said solid fuel material.
 2. The suspension according to claim 1, further comprising a liquid fuel component.
 3. The suspension according to claim 1, wherein the dry granular solid component, or solution thereof, is, or contains, an oxidizer.
 4. The suspension according to claim 3, wherein the oxidizer is ammonium nitrate.
 5. The suspension according to claim 2, wherein the liquid fuel component is a fuel oil or diesel fuel.
 6. The suspension according to claim 5, wherein the amount of the liquid component is about 0-10% by weight percent.
 7. The suspension according to claim 1, wherein the amount of the vitrinite maceral in said solid fuel material is about 75 weight percent.
 8. The suspension according to claim 1, wherein said solid fuel material is present the amount of about 5 to about 80 weight percent.
 9. The suspension according to claim 1, where said suspending agent is a polymeric or nonpolymeric emulsifying agent, or mixture thereof.
 10. An explosive suspension comprising: a dry, granular, solid oxidizer component, or solution thereof, a liquid fuel component, a solid fuel material, and a suspending agent, wherein the liquid component is present not more than about 6% by weight and wherein said solid fuel material is coal containing vitrinite and liptinite macerals.
 11. The suspension according to claim 10, wherein the oxidizer is ammonium nitrate.
 12. The suspension according to claim 11, wherein the liquid fuel component is a fuel oil or diesel fuel.
 13. The suspension according to claim 10, wherein the amount of vitrinite macerals in said solid fuel material is about 75 weight percent of the solid fuel material.
 14. The suspension according to claim 13, wherein said solid fuel material is present in the amount of about 5 to about 80 weight percent.
 15. The suspension according to claim 10, wherein said suspending agent is a polymeric or nonpolymeric emulsifying agent, or mixture thereof.
 16. An explosive suspension comprising an oxidizer component, a liquid fuel component, a solid fuel material, and a suspending agent, wherein said solid fuel material is coal containing vitrinite and liptinite macerals. 